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MCD - Diagnostics > Bacteriology > Flashcards

Flashcards in Bacteriology Deck (10):
1

How is MIC tested?

least amount of antibiotics required to inhibit growth

Gradient antibiotic strips on agar - look for crossover of bacteria on the strip

Discs impregnated with different conc of antibiotic. Measure clerance zone guidelines have zone sizes on how this translated to MIC

2

What kind of investigations may be performed?

culture e.g. agar or a broth
Serology
Molecular techniques

3

What are the complications of starting patients on antibiotics before sending off samples?

The antibiotics can interfere with the test results - potential for false negatives as the dose administered may not have a clinical effect but it might have an effect at the cellular level on the agar

In meningitis or sepsis you administer anyway

4

What kind of samples might be used?

stool samples, mouth & vaginal swabs, taking blood

5

Describe susceptibility testing

Still use agar plates and MICs, takes about 18 hours

6

Describe how blood cultures are run

Different bottles for collection
pH indicator on bottom of bottle changes colour as pH lowered from bacteria producing CO2
takes about 18 hours

7

What kind of microbiological tests might be carried out?

Gram staining - double membrane are negative, single membrane are positive (peptidoglycan retains purple dye)

Microscopy - look at shape and organisation (clumping or chains)

Coagulase e.g. staf aureus is positive but other stafs are negative

8

What are the limitaions of microbiological investiagtions


slow - some e.g. TB can take 6 weeks to grow

MIC tests difficult to interpret

9

Explain the results of MIC

3 types of result resistant intermediate sensitive

guideline values for MIC enables the lab to say whether its sensitive or resistant – resistant because not enough of the drug will be able to reach the organisms. Guidelines have cross over values and zone sizes

10

What are the limitations of PCR?

-need to know what looking for to design primers
-potentially hundreds of primers needed as many genes confer resistance
-PCR less sensitive than culture